1. Field of the Invention
This invention relates to a method of stacking metal sheet materials, particularly photosensitive printing plate precursors.
2. Description of the Prior Art
In conventional lithography, a photosensitive printing plate precursor comprising a metal support, such as an aluminum plate having a hydrophilic surface, with a photosensitive layer thereon is imagewise exposed and processed with a developer to form a resist layer from which exposed areas or unexposed areas have been removed. The printing plate thus prepared is set in a printing machine and used with oily ink placed on the plate after applying dampening water to the exposed hydrophilic metal surface having no resist layer.
Photosensitive lithographic printing plate precursors are cut to a predetermined size, stacked on top of each other and packed in a predetermined number for shipment. Photosensitive lighographic printing plate precursors or printing plates prepared therefrom are also usually stacked on top of each other for storage prior to use. in either case, adjacent precursors or plates have interposed therebetween a protective interleaving paper sheet or some other type of interleaf that intimately contacts the surface of the photosensitive layer or plate. One example of a material for such an interleaf is paper coated with plastic on both sides.
In conventional techniques, intimate contact between an interleaf and the surface of the photosensitive layer of an uncut or cut photosensitive printing plate precursor is obtained electrostatically by applying a high voltage to the surface of the photosensitive layer. Details of such a method and apparatus for implementing this technique are given in German Patent Applications (OLS) Nos. 1,452,935 and 1,552,110. However, residual static electricity of high voltage often accumulates on interleaves made of paper with plastic coated on both sides to give an electric shock to users or persons who handle the stacked precursors.